1. Field of the Invention
The present invention relates to thin-film magnetic heads for writing information onto a magnetic recording medium and, more particularly, to a magnetic recording head having a plurality of insulator layers.
2. Description of the Related Art
FIG. 8 through FIG. 10D show the conventional technique used in this sort of the magnetic recording head. Referring to FIG. 8, a thin-film magnetic head 21 includes a gap layer 23 made of alumina, a first insulator layer 24 made of an organic insulating material, and an electrically conductive spiraling coil layer 25 made of an electrically conductive low-resistance material such as Cu, successively laminated in that order on a lower magnetic core layer 22 fabricated of a magnetically soft material such as an Fe—Ni based alloy (permalloy). A second insulator layer 26, made of an organic insulating material, for covering the electrically conductive coil layer 25 is formed on the first insulator layer 24. An upper magnetic core layer 27 made of a magnetically soft material such as an Fe—Ni based alloy is formed on the second insulator layer 26. A linear pole region 28 of the upper magnetic core layer 27 covers slopes 24a and 26a of the first and second insulator layers 24 and 26 at the respective end faces thereof, and the top of the end portion of the gap layer 23.
A magnetic gap 30 is formed between the lower magnetic core layer 22 and the upper magnetic core layer 27 at the end 29 facing a medium. The distance between the medium facing end 29 and the front end of the first insulator layer 24 is a gap depth Gd. The gap depth zero position is defined by the front end of the first insulator layer 24. The upper magnetic core layer 27 is narrower in width than the lower magnetic core layer 22. Referring to FIG. 9, the narrower end portion of the pole region 28 has a track width Tw. The track width Tw is thus defined by the width of the front end portion of the pole region 28 of the upper magnetic core layer 27.
When the electrically conductive coil layer 25 is supplied with a recording current in the thin-film magnetic head 21 thus constructed, a recording magnetic field is induced between the lower magnetic core layer 22 and the upper magnetic core layer 27. A leakage magnetic field leaked from the magnetic gap 30 at the medium facing end 29 thus writes information onto a magnetic recording medium.
The thin-film magnetic head 21 is manufactured in a process sequence as shown in FIGS. 10A through 10C. Formed on the lower magnetic core layer 22 are the gap layer 23, the first insulator layer 24, and the second insulator layer 26. Referring to FIG. 10D, an underlying layer 31 made of a magnetically soft material such as an Fe—Ni based alloy is plated over from the front end portion of the gap layer 23 to the second insulator layer 26. A resist layer 32 is then applied on the plated underlying layer 31. Using photolithographic technique, the resist layer 32 is subjected to exposure and development processes to partially remove the resist layer 32. The resist layer 32 thus has a pattern corresponding to the upper magnetic core layer 27 including the pole region 28. The pattern having no resist layer 32 is electroplated, thereby forming the upper magnetic core layer 27 and the pole region 28. Removing the residual resist layer 32 completes the production of the thin-film magnetic head 21.
In this conventional thin-film magnetic head 21, the first insulator layer 24 is formed on the gap layer 23, and the second insulator layer 26 is formed on the first insulator layer 24. The thickness T1 from the top surface of the gap layer 23 to the top surface of the second insulator layer 26 is large. Since the resist layer 32 to be applied onto the plated underlying layer 31 is flowable, the thickness T2 of the resist layer 32 becomes large on the top of the end portion of the gap layer 23 to the slopes 24a and 26a of the first and second insulator layers 24 and 26. In this area, a resolution of the photolithographic technique is substantially degraded. As a result, the dimensional accuracy of the pattern of the resist layer 32 is greatly lowered. The width of the front end portion of the pole region 28 of the upper magnetic core layer 27, namely, the track width Tw is not formed with a high accuracy. A narrower track is difficult to produce.
When the resist layer 32 is patterned through the photolithographic technique, a light beam to which the resist layer 32 is exposed is reflected diffusely from the slopes 24a and 26a formed at the end faces of the first and second insulator layers 24 and 26, thereby distorting the pattern. The front end portion of the pole region 28 of the upper magnetic core layer 27 is not produced to a predetermined track width Tw with a high accuracy. This problem is resolved by extending the pole region 28, namely, by receding the first and second insulator layers 24 and 26 in the back portion of the upper magnetic core layer 27 in the direction represented by an arrow Y. This arrangement causes a gap depth Gd to be lengthened, thereby adversely affecting information writing characteristics such as overwrite characteristics to the magnetic recording medium.
FIG. 11 is a graph plotting the results of measurement of the track width Tw of a plurality of thin-film magnetic heads 21. The track width of the thin-film magnetic head 21 substantially varies with respect to a rated 0.57 μm and there are many thin-film magnetic heads 21 having the track widths thereof out of the rated track width.